During myeloid differentiation granulocyte precursors develop the ability to perform the functions of mature cells. We have a continuous cell line from a patient with promyelocytic leukemia, HL-60, which, under the influence of dimethylsulfoxide, differentiates into mature-appearing granulocytes. We propose to determine the developmental pattern of functions associated with phagocytosis, namely mobilization, chemotaxis, recognition, ingestion, oxidative metabolism and bacterial killing. We hope to determine when in the course of myeloid differentiation each function appears. We also plan to determine the developmental pattern of granulocyte enzymes involved in these processes. In addition, using pulse labeling techniques, we plan to study the time at which specific proteins associated with phagocytic function appear (e.g., actin, myosin and actinbinding protein). Membrane properties, such as fluidity, will be studied by polarization fluorescence and will be correlated with studies on the protein composition of the membrane. We also plan to investigate the relationship of cell division to differentiation using antimetabolites and determine aspects of myeloblastic differentiation. We also plan to examine differentiation in other established cell lines and attempt to establish continuous lines from other promyelocytic leukemic cells.